The present invention relates to an electric machine that can be mounted in or on a retaining device, for example a machine frame.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
If, for example, a torque motor is to drive a separately mounted work machine without a coupling connection on the shaft side, then over-determined bearing will occur. Over-determined bearing of such kind can be successfully avoided by using torque supports that absorb the stator's reaction torque and duct it into the machine frame. The stator is otherwise linked to the machine only via the motor bearings. The bearings absorb the motor's static forces. The torque support absorbs only the counter-torque to prevent the stator from speeding up under the influence of said counter-torque.
It has hitherto been customary to use single-arm torque supports which, while ensuring a low degree of rigidity in the three translational axes, are far more rigid for rotations. A force whose counter-forces will have a damaging impact on the motor bearings will hence be transmitted at the securing point between the torque support and machine frame. Especially the motor bearing closest to the motor support will absorb the greatest portion of said force. That design also has further disadvantages for controlled dynamic operation because types of vibration that are not pure torsion vibrations will also be induced in that way by the counter-forces.
Another disadvantage of the single-arm torque support is its lack of potential to achieve a greater degree of torsional rigidity. Finite-element simulations have shown that even ideally stiffening individual elements (wobble stick, motor bearing, stator housing) will produce only a slight increase in torsional rigidity. That characteristic can be explained by the vibration pattern occurring in the case of a single-arm torque support. When resonance occurs it is not just the rigid stator that vibrates via the elastic wobble stick on the torque support but also the two motor bearings and the motor shaft. Moreover a twisting of the stator housing is even discernible. The effectively acting torsional rigidity therefore acts like a plurality of springs connected one behind the other, the overall effect of which is an ever-reducing rigidity.
It would therefore be desirable and advantageous to provide an improved electric machine to obviate prior art shortcomings and to keep introduction of reaction forces into the motor bearings during operation to a minimum.